Method for Manufacturing CIGS Thin-Film Solar Cells Using Substrates Not Containing Sodium

Researchers at the Korea Institute of Energy Research (KIER) have developed an innovative method for manufacturing CIGS thin-film solar cells using substrates not containing sodium. This technology specifically relates to a method for manufacture in which Na (sodium) supply sources are formed on parts of the surface of molybdenum electrode prior to the formation of CIGS-based precursor thin film and then heat-treated to form CIGS-based thin film. Thereby improving the electrical characteristics of the CIGS-based thin film serving as a light-absorbing layer of a solar cell, and to CIGS-based thin-film solar cell manufactured using the method.

This advanced technology is particularly valuable in response to the increasing attention being placed on alternative next-generation clean energy sources. As such, greater scientific research is being paid to fossil fuel alternatives, such as solar cells. Solar cells directly converting sunlight into electric energy have various merits such as avoidance of contamination, infinite resource and semi-permanent lifespan, and are thus anticipated as an energy source capable of solving the problem of energy depletion.

Solar cells are classified according to the materials used in light-absorbing layers. Among these solar cells, silicon solar cells are most frequently used. However, the price of silicon solar cells has rapidly increased due to a supply shortage of silicon, and thus thin-film solar cells have attracted considerable attention. A thin-film solar cell is used in a wide range of fields because it requires less raw material consumption and is lightweight. A CIS or CIGS-based thin film semiconductors exhibits the highest conversion efficiency among lab-made thin films. Particularly, since CIS or CIGS-based thin films are characterized in that they can be formed to a thickness of 10 mm or less and are stable even after long-term use. It is predicted that CIS or CIGS solar cells will be used in manufacturing as a low low-priced high-efficiency alternative to commonly used silicon solar cells.

CIGS- based thin film was developed to improve the low open voltage of a CIS-based thin film, and is a material prepared by replacing a part of Indium (In) with Gallium (Ga) or replacing Sulphur (S) with Selenium (Se). CIGS-based thin film is generally prepared by forming molybdenum electrode on a soda-lime glass substrate, forming CIGS based precursor thin film on the molybdenum electrode and then performing a selenization process. In this case, it was found that, during the selenization process, Na ions existing in the soda-lime glass substrate are diffused into the CIGS-based thin film, thus improving the electrical characteristics of the device. However, it is impossible to control the diffusion of Na ions into the CIGS-based thin film. Therefore, to control the diffusion of Na ions, an anti-diffusion layer for preventing the diffusion of Na ions into the CIGS-based thin film from the soda-lime glass substrate must be used.

Prior research focusing on CIGS manufacture advancements have encountered significant limitations, such as deterioration in the electrical characteristics (conductivity) of molybdenum, difficulty in uniformly diffusing Na and generally lengthening the CIGS thin-film manufacture process.  The present technology, developed and presented by the KIER, has been devised to solve the inherent problems related CIGS thin film manufacture and establish an improved method of manufacturing CIGS-based thin-film solar cells. This sophisticated CIGS thin film manufacture method boasts improved efficiency and reduced production costs. 

Method for manufacturing CIGS thin-film solar cells using substrates not containing sodium:

This streamlined method for manufacturing CIGS thin-film solar cells using substrates not containing sodium film is achieved through the completion of several intricate steps:

• Step 1: Forming molybdenum electrode on Na-free substrate; The Na-free substrate used may be a polymer substrate selected from the group consisting of polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES) and aromatic polyester (liquid crystal polymer); a stainless steel (STS) substrate; a Na-free glass substrate or a ceramic substrate.
• Step 2: Forming Na supply sources on parts of the surface of the molybdenum electrode. A solution containing a Na supply source may be selectively applied and then dried. The solution may be applied by spray coating, ink-jet printing or spin coating using a mask. The Na supply sources may be formed on a part of the surface of the molybdenum electrode using a mask in a vacuum chamber or the sources may be sodium halide.
• Step 3: Forming CIGS-based precursor thin film on the molybdenum electrode. The CIGS-based precursor thin film may be formed by any one non-vacuum coating selected from the group consisting of spraying, ultrasonic spraying, spin coating, a doctor blade method, screen printing and inkjet printing.
• Step 4: Heat-treating the CIGS-based precursor thin film with selenium to diffuse Na from the Na supply sources into the CIGS-based precursor thin film, thus forming a CIGS-based thin film. The heat treatment with selenium may be performed at a temperature of 250 ∼ 600°C for 30 ∼ 120 minutes under a selenium atmosphere.

Intellectual property status

Granted Patent

Patent number : 2693496

Where : European Patent

Current development status

Commercially available technologies

Desired business relationship

Technology selling

Patent licensing

Joint ventures

Technology development

New technology applications

Adaptation of technology to other markets